Temperature control apparatus for cabins of aircraft



June 28, 1949.- H. 1-. SPARROW 2,474,441

TEMPERATURE CONTROL APPARATUS FOR CABINS 0F AIRCRAFT Filed June 6, 1946IN VEN TOR. All/our r smmrow sor of said engine or turbine. more thanadequate pressure and because of its Patented June 28, 1

TEMPERATURE CONTROL APPARATUS FOR CABINS OF AIRCRAFT Hubert T. Sparrow,

Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Company,Minneapolis, Minn., a corporation of Delaware Application June 6, 1946,Serial No. 674,748

17 Claims.

The present invention relates to apparatus for controlling temperaturein the cabin of an aircraft supplied with ventilating air underpressure.

The ventilating air for. the pressurized cabin of an airplane propelledby a jet engine or a gas turbine is conveniently taken from the compres-Thls air is under heat of compression, no other heaters are needed.However, because the heat of compression of this air is generallyexcessive for the needs of the cabin, cooling must be provided to keepthe temperature within the desired limits. Although air for cooling isplentiful, it is preferable to minimize the use of aftercoolers and thelike because of their interference with the aerodynamic characteristicsof the airplane. For this reason, refrigerating means are provided forcooling the air to be used for cabin ventilation, with aftercooler meansbeing provided to supplement the said refrigerating means.

It is therefore a principal object of this invention to provide meansfOr properly controlling aftercooler and refrigerating means used for,

cooling air supplied to an aircraft cabin.

It is also an object to provide means for controlling a plurality oftemperature changing means in a predetermined sequence.

More specifically, it is an object to provide means for controllingaftercooler means and refrigerating means in such manner that theprincipal cooling load is carried by the refrigerating maintaining therate of air inflow to a structure equipment and the aftercooler means isused to supplement the refrigerating means.

Additionally, it is an object to provide means for controlling theaftercooler means and refrigerati'ng means so that light cooling loadswill be handled by the aftercooler means, ordinary cooling requirementswill be met by the refrigerating means, and large cooling loads will behandled by both the refrigerating means and the aftercooler means,

Further, it is an object to provide control apparatus of a sort whereina plurality of devices are so controlled that one device is firstoperated to meet a demand; upon further demand a second device is usedand assumes the full load, the first device being made inoperative, andupon a still {further increase in load, both devices are used.

When the air for cabin ventilation and pressurizing is taken from thecompressor of the power plant for aircraft, it is obvious that the saidpower plant is deprived of the air with a consequent loss of power. Itis thus desirable to use at a predetermined value under most conditionsbut wherein the said value may be increased to meet extreme conditionsof either heat or cold in the said structure.

These and many other objects will become apparent upon a study of thefollowing specification and drawings:

The single figure of the drawings shows schematically the presentinvention as applied to an aircraft equipped with a jet engine.

In the drawing, aircraft cabin i0 is supplied with ventilating airthrough conduit H which receives air from the compressor of a jet engineshown schematically at l2. The air delivered to cabin I0 is exhaustedthrough pressure regulating valve means, not shown. To control the rateof air flow through duct II, a butterfly valve or damper means 13 isprovided which is oper-- ated through suitable linkage means M byreversible motor means l5. Motor means I5 is a conventional two-phasegeared motor of the sort wherein a suitable capacitor is connected inseries with one or the other of the windings to cause reverse operation.Preferably, this motor is also equipped with internal limit switch orstop means to limit the operation of the motor in either direction.

Venturi means It is located downstream of valve means l3 and serves as alimiting device and a sensing device to determine the rate of-air flow.A differential pressure controller l1, connected in controllingrelation'to motor means I5,

is actuated in response to the pressure differences existing across theentrance and the throat of the Venturi means i6. Tube l8, connected toduct II at the entrance to venturi i6, is connected to expansiblebellows means l9 of controller I1, and tube 20, connected to thethroatof venturi I6, is connected tojbellows means 2| of controller I].Bellows means l9 and 2| coact in opposing relation with lever means 22which is pivoted about knife edge pivot means 23. At its left extremity,

lever means 22 includes an electrically insulated portion 24 and movablecontact means 29, the said contact means 29 coacting with stationarycontacts 29 and 21. A tension spring 20 is connected to the rightextreme of lever 22 and is adjusted by lever means 29, pivoted at 90,and adjustably operated by cam means 9| coacting with a follower 42 atthe opposite end of lever means 29. Cam means 3| is carried on shaft 33of motor means 94, to be described. Cam means 9| includes a high portion99, a low portion 89, and suitable inclined portions connecting the highand the low portions. The function of this cam will be later described.

The air taken from the compressor of a jet engine, for example, may becompressed to several atmospheres and consequently is at a relativelyhigh temperature. To cool the air flowing through conduit II to cabinI0, an aftercooler means 40 is provided. Aftercooler means 40 comprisesa simple heat exchanger having two sets of passages, conduit IIconnecting with one set of' passages and cooling air from conduit 4Iflowin through the other set of passages. This cooling air is obtainedthrough a suitable ram air inlet, not shown, and is discharged at apoint where it will have the least effect on the aerodynamiccharacteristics of the airplane. The flow of cooling air throughaftercooler 40 is controlled by a suitable damper means 42 connected bya suitable linkage 43 to motor means 44. Motor means 44 is a geared twophase motor similar to motor means I5, but differing therefrom in thatit also drives a follow-up potentiometer wiper 45 by shaft 49.

In addition to aftercooler means 40 for cooling the air delivered tocabin I9, refrigerating means 90, in the nature of an expansion turbine,is provided. The refrigerating means per se forms no part of the presentinvention, hence it has not been shown, but it may be mentioned that anexpansion turbine provides cooling by permitting a compressed gas, suchas the air in the present case, to expand through the same with workbeing done by the turbine. The work or energy available from the turbinemay be used for increasing the rate of air flow through aftercooler 40,for driving auxiliary apparatus, or it may be wasted. To provide simplemeans for controlling the cooling effect of refrigerating means 50,bypass means is provided. A diverting damper or valve means 92 controlsthe flow of air through either bypass means 5i, refrigerating apparatus00, or proportions the air flow through both of the said means. Dampermeans 52 is operated by linkage 53, which in turn is operated by gearedmotor means 54. Motor means 54 is similar to the aforesaid motor meansis and 44 but it not only drives potentiometer wiper 55 through shaft59, but also operates switch means 51 by means of a cam 59 carried onsaid shaft 99.

Motor means 44 is controlled by amplifier means 90 and motor means 54 iscontrolled by amplifier means 9|. Amplifier means 90 and 9| may be ofany conventional sort suitable for controlling a motor and wherein thephase relation of the output voltage is similar to the phase of theinput signal. with this sort of an amplifier, when there is no inputsignal, there is no output signal, but when there is an input signal ofone phase rela tion, the output signal will be of like phase relationand will energize one winding of motor 44 and cause operation of themotor in one direction, the other winding being energized from a linesupply, as will be pointed out later. If the input signal should be ofopposite phase, then the output signal would likewise be of oppositephase, the winding of the motor would be energized in a different mannerand reverse operation of the same would take place. As an example ofamplifiers of this sort, reference is made to the copending applicationof Albert P. Upton, Serial No. 437,561, filed April 3, 1942, now PatentNo. 2,423,534 granted July 8, 1947. As noted, motor means 54 iscontrolled by amplifier means 9|, and the remarks made relative toamplifier and motor 44 hold equally well for amplifier GI and motormeans 94.

Amplifiers 90 and 6| are controlled by an electrical network generallydesignated as 69. Network 99 is energized through input terminals 04 and99 connected to secondary 99 of transformer 91. Primary winding 99 oftransformer 91 is connected to line wires by suitable connections, notshown. The network circuit is, in series from input terminal 94,resistor'10, adjustable wiper 1I coacting with said resistor 10, fixedresistor 12, resistor 13 of rebalance poteniometer 14, resistor 19 ofrebalance potentiometer 19, fixed resistor 11, input terminal 95, wire90, temperature responsive resistor, or thermistor, 8i located in thedischarge portion of duct II, wire 92, resistor 99 of potentiometer 94,wire 99, and fixed resistor 99 back to input terminal 94. An adjustableresistor 19 is connected in parallel with resistor 13 for adjusting thepotential drop across the same and a simi-' lar adjustable resistor 19is connected in parallel with resistor 15. Potentiometer wiper 91coacting with resistor 89 is carried on and adjusted by shaft 99 in amanner to be described. Wiper 91 forms one output terminal of network 99and wipers 49 and 99, coacting with resistors I3 and 15, respectively,form other output terminals of the network.

In addition to network 63, an overlap network 90 is also connected incontrolling relation to amplifier GI. This network comprises apotentiometer 9I having its resistor 92 connected in series with switch51 and secondary winding 93 of transformer 94 by wires 99 and 99. Wiper95 of potentiometer 9| is connected to input terminal 99 of amplifier 6|by wire 91 and wire 99 is connected to wiper 59 by wire 209.

It has been previously noted that cam 3| and wiper 91 are each carriedon shaft 33 which is driven by a motor means 34. Motor means 34 is ageared two phase motor similar in construction to the aforementionedmotors I5, 44 and 54. Motor means 34 is controlled by a suitableamplifier IOI which is preferably similar to ampliilers 60 and BI,previously described.

Amplifier means IOI is controlled by an electrical network circuit I02.Input terminals I03 and I04 of network I02 are energized by secondarywinding I05 of transformer I06. Primary winding I01 of said transformeris connected to line wires I09 and H0 by suitable connections, not

, shown. The upper left-hand branch of the network comprises inputterminal I09, resistor II3, wire H4, and the portion of resistor II8lying to the left of adjustable contact III. The upper righthand branchof the network comprises the portion of resistor I I6 lying to the rightof contact III, wire III, temperature responsive resistor, orthermistor, II1, wire H9 and input terminal I04. The lower right-handbranch of the network comprises fixed resistor H9, and the portion ofresistor I2I lying to the right of wiper II2. The lower left-hand branchof the network comprises the portion of resistor I2I lying to the leftof wiper I I2, adjustable resistor I20 for determining the control pointof the network, and fixed resistor I22 back to input terminal I03.Adjustwith resistor III so that the able contact I I I forms one outputterminal of network I02 and wiper II2, carried by theaforesaid shaft 38,forms the other output terminal of the network. A rheostat I23 isconnected in parallel potential across resistor |2I can be varied.

To provide electrical energy for the various components of the presentsystem, line wires I69 and H are connected to a suitable source ofalternating current. Transformer I30 has its secondary winding |3|connected to motor means I and has its primary winding I32 connected tothe line wires by the circuit: line wire I09, wire I32,

primary winding I 33, wire I 36 and line wire IIO. Transformer I36 has apair of secondary windings I31 and I38 for amplifier 60 and motor means44, respectively, and its primary winding I60 is energized by thecircuit: line wire I09, wire I39, primary winding I60, wire I and linewire IIII.

Transformer I62 has secondary windings I43 and I for energizingamplifier 6| and motor mean 56, respectively, and its primary winding M6is energized as follows: line wire I09, wire I45, primary winding I66,wire I41 and line wire H0. The primary winding |5| of transformer 93 isenergized by the circuit: line wire I09, wire E50, primary winding I5I,wire I52, and line wire iii'i. Transformer I56 is similar totransformers I36 and I62 and has secondary windings I55 and I 56 forenergizing amplifier I 0| and motor means 38, respectively, while theprimary winding I58 is energized by the circuit: line wire I89, wireI51, primary winding I58, and wire I59 to line wire I I0.

To more fully explain the function of the present apparatus, referenceis made to the following schedule of operation.

Operation ing the power plant of the airplane, assume that I line wiresI09 and H0 are suitably energized by alternating current.

Before going further with this description, it

' will be noted that the apparatus is energized by alternating currentand that network circuits are used to control the present amplifiers. Itis well-known that circuits of this sort control their associatedamplifiers by signals of one phase when the network is unbalanced in aparticular way and by signals of an opposite phase when the networks areunbalanced in the opposite direction. However, it is rather confusing todescribe the present network circuits and the like in terms of theirphase relations and, as it has been found much more convenient todescribe the present circuit in terms of the potentials existing at thetime oi a half cycle, this description shall proceed on that basis.Therefore, rather than describe the phase of a signal from network 63 orI02, it will be discussed in terms of its positive or negativepotential, it being kept in mind that this is merely a convenient mannerof describing the actual phase relations which are present. At theinstantof the half cycle in question, it may be assumed that the leftsides of networks 63 and 6 I02 are positive relative to the right sides.Further, the lower end of resistor 92 may be considered positiverelative to the upper end of the same.

It was previously noted that'the temperature in cabin 10 of the aircraftwas about 73 degrees, hence the temperature at thermistor I I1 may beassumed to be at that value. If it now be further assumed that theresistance values of network I02 are such that wiper 2 must be at theextreme left of resistor |2| to balance the network when the temperatureat I" is degrees and the wiper must be at the extreme right of resistorI2I to balance the network when the temperature at 1 is at 65 degrees,then with a temperature at 117 of '73 degrees and with wiper H2 at aboutthe midpoint of resistor I2I, it appears that network I02 is balanced.Although network I02 is supplying no signal to amplifier IOI, it isnoted that wiper H2 is connected by wires I16 and ill to input terminalI15 of the amplifier, wire I16 also being connected to ground throughwire I18. Further, adjustable contact III is connected by wire I19 tothe other input terminal I80 of the amplifier. The amplifier IOIreceives its energizing current from transformer secondary winding I55through wires I12 and I13 and the motor 36 is energized from theamplifier and from secondary winding I56 by the circuits: winding I56,wire I8I, motor terminal I82, terminal I83, wire I86, wire I85,capacitor I86, wire I81 and winding I56. This energizes the winding ofthe motor connected between terminals |82 and I83. The other winding ofthe motor is energized by the circuit: output terminal I89 of theamplifier, wire I90, wire I88, terminal I83, terminal I88 and wire |9|to the other output terminal I92 of the amplifier. It is thus noted thatthe first mentioned winding of motor 34 is constantly energized throughcapacitor I86 by winding I56 but the other winding of the motor iseffectively energized only when there is an output from amplifier I 0|.Further, the direction of rotation of motor 36 depends on the phaserelation or, in

this description, the potential of the amplifier output. Since only onewinding of motor 36 is energized,.the motor does not operate and wiper 2remains in its mid-point adjustment. It is noted that motor 34 not onlyadjusts wiper 2 but that it also adjusts wiper 81 associated withnetwork 63 and cam 3| associated with the airflow control apparatus, thesaid cam and wiper 81 being carried on shaft 33 of the said motor Withwiper H2 at an intermediate position, cam 3| is also adjusted to anequivalent intermediate position and therefore follower 32 of lever 29is on low portion 36 of the said cam.

With differential pressure controller I1 adjusted for a low rate of airflow by cam 3|, it is nevertheless noted that there is no air fiow atthis time to control. With no air flow through duct II and venturi I6,the pressure in bellows I9 and 2| is equal hence lever 22 is rotated ina' I66, capacitor I61, wire I60, wire I60, terminal 110, terminal I64and wire I66 which is common to the two windings. It is noted thatcapacitor I61 is in the circuit which energizes the winding connectedbetween terminals I10 and I64. With both windings of motor I6 energizedas above described, the said motor is caused to rotate in a clockwisedirection but, since damper I3 has already been rotated in a clockwisedirection to its full open position, further rotation is prevented bythe limit means of the motor.

With line wires I08 and M energized, transformer 61 of network 63 islikewise energized due to connections, not shown, from primary winding66 to the said line wires. As before noted, the energizationis such thatinput terminal 64, during the half cycle, is positive relative to inputterminal 65. In addition, amplifier 60 is furnished energizing currentirom transformer secondary winding I31 by wires M0 and 2H, and amplifierSi is likewise energized from transformer secondary winding its by wires225 and 226. In addition, motor means it is energized by the circuits:transformer secondary winding 536, wire 2I2, motor terminal 263,terminal 258. wire 2I5, wire 2i6, capacitor ,illl, wire sis and windingM6; the other winding of the motor is energized from amplifier Bil bythe circuit: output terminal 224, wire 223, wire tilt, terminal 2 l s,terminal 222, wire 222i output terminal 22s. Also, motor means El i isenergized my the circults: transformer secondary winding GM, Wire 227,motor terminal 228 terminal 22s, wire 23o, wire 23L capacitor 232, wireand winding B i l; the other winding of the motor energized by thecircuit: output terminal or amplifier all, wire 23'i, tern-natal 238,terminal 22%, Wire wire 23% and the other output terminal E li! oiamplifier (ii. if it now he assumed that wiper S s at approximately themiezl-pcint or resistor and that network to is so adjusted and call".srated that wiper El must he at the extreme left resistor 83 tobalance the network when thermister 8! is at so degrees, and must he atthe extreme right of resistor 83 to balance the network when thermistorEll at sea degrees, it then appears, due to the mid=point adjustment,that the network will he salanced as shown. ii temperature at ill isabout 125 degrees. was noted, however, that the temperature at SM isabout 73 degrees hence it follows that network not balanced. Withthermistor [ll relatively cool, and therefore resistance relatively low,the potential of input terminal 35 is closer to that of wiper ill thanit would'otherwise be. Therei'ore, since the potential differencebetween input terminal 653 and 55 remains the same at all times bothwipers G and "oecorne more positive relative to wiper ill as wiper illapproaches terminal 55 in potential. As the network is originallyadiusted so that the potential at wiper '55, ignoring network ilmwouldbe the same as the potential at wiper 3'! when the network is balanced,with wiper 55 in the position shown, then it follows that wiper 45 willalways be more positive than wiper 55. With wiper 45 positive relativeto wiper 81, a positive signal is impressed on amplifier 60 by thecircuit: input terminal I of amplifier 60, wire 203, wire 202, wiper 81,network 63, wiper 45, wire 200 and input terminal 201 of the amplifier.It is noted that input terminal 20I of the amplifier is grounded throughwires 203 and 206. With the motor winding connected between motorterminals 2I3 and 2 being energized directly from transformer sec- 8ondary winding I36, and with the other winding of the motor beingenergized from amplifier 60 when there is a signal impressed on the saidamplifler, it is noted that there is energization of the other winding0! the motor due to the functioning of the amplifier, hence motor 44tends to rotate in a counter-clockwise direction. However, it is notedthat damper 42 has already been rotated to its maximum counter-clockwiseposition hence mrther rotation is prevented by stop means associatedwith the motor. Although wiper 55 is obviously negative relative towiper 46, it is also noted that under the conditions stated that thesaid wiper 65 is positive relative to wiper 81 and therefore a positivesignal is impressed upon amplifler Si by the circuit: input terminal 204of the amplifier Si, wire 205, wire 202, wiper 8'1, network 63, wiper55, wire 209, wire 98, the upper portion or resistor 92, wiper 55, wire9'! and input terminal 98 of the amplifier. It is noted that wiper 55 isnot directly connected to amplifier terminal 98 but rather is connectedthrough network 50. Since switch 51 is in a position wherein itscontacts are closed, network is energized and, as it was previouslystated, when network {it is energized wiper is positive relative towiper S5. The wiper 95 is adjusted on resistor 92 so that the said wiperis positive relative to wiper 65 an amount equal to the potential dropacross resistor it plus a predetermined pare age, such as about 15 percent, or resistor Therefore, although wiper 55 is positive relative towiper ill, the potential impressed on input ter-- minal 95 isconsiderably more positive relative to the wiper due to network 90. Asmotor 5i was prewously noted to he energized from trans-- former winding4 and amplifier Ill such fashion that any suflicient output voltageamplier 6i would cause operation or the motor, it is now noted thatthere is such an output from the amplifier hence motor 54 tends tooperate a counter clockwise direction. However, sine: damper 52 isalready in its maximum counterclockwise position, further operation ofthe same in counterclockwise direction is prevented by sto; meansassociated with the motor means 54.

11 the power plant of the aircraft is now started air is sled from thecompressor of the same b: conduit ii. With the parts in the positionshown a maximum rate of airflow will be permitted am there will he nocooling by either the aftercoole ill or the expansion turbine 50. Thefirst efiec clue to this airflow will be noticed at the airflo controlapparatus. With a relatively high rat 0i flow now taking place throughventuri 16, th pressure in bellows 89 will be considerably in creasedover that in bellows 2i and, when tli pressure in bellows I9 issuificient to overcome ti: efforts of bellows 2i and spring 28, lever 22wi be rotated in a counterclockwise direction an contacts 25 willdisengage from contact 26. Who the differential pressure is sufiicientto move cor tacts 25 into engagement with contact 21, HIGH means I5 willbe energized by the circuit: win ing l3l, wire I60, insulated portion 24of lev v22, contacts 25, contact 21, wire 245, wire I6 motor terminalI10, terminal I64, wire I65 a: winding I3 I The other winding of themotor w be energized by a similar circuit, starting fro wire 245 asfollows? wire I68, capacitor I61, wi I66, wire I62, terminal I63,terminal I64 a1 common wire I65. This energization of mot means I5differs from that by which the mot was previously energized in that thecapacit I6! is now in the circuitenergizing the windi:

connected between terminals I 64 and I". This causes motor means I tooperate in the opposite, or counterclockwise direction thereby movingdamper IS in a closing direction. 'As damper i3 moves in a closingdirection, the airflow across venturi is diminished and therebydecreases the diflerential pressure affecting controller i1.

When the difierential pressure diminishes sumor 21 to cause furtheradjustment oi the said damper. Assuming that damper l3 will be operatedin accordance with controller H to maintain the desired rate of airflow, it may now be recognized that not only is an airflow establishedto cabin l0 through duct H but also heat is being.

supplied due to the heat of compression possessed by the compressed air.

Assuming for the moment that the temperature in cabin it has not beenchanged by this heated air being supplied to the same, it will be notedthat the most immediate efl'ect of the temperature change in the air isto increase the temperature of thermistor 8|. of thermistor 8|increases, and therefore its resistance is increased, wiper 81 becomesmore positive relative to input terminal 65 and also to wipers 45 and55. Therefore, theunbalance of the network is decreased.

If it now be assumed that the aircraft starts its As the temperature.

flight and is climbing rapidly, and still assuming that the temperaturein cabin Ill remains at approximately 73 degrees, it will now be notedthat the high output being demanded from the power plant l2 results'in aconsiderable compression of the air by the compressors of the engine.This compression also results in considerable heat being added to theair and, with damper l3 controlling the rate of flow to the cabin, theheat input to the cabin is increased due to the high temperature of theair. However, the first effect of the high temperature is at thermistor8| which is increased in temperature, and its resistance thereforefurther increased. As the temperature of thermistor 8i rises above thecontrol point of 125 degrees, wiper 55 becomes negative relative towiper 87. .Iowever, since input terminal 96 is positive relative towiper 55 by a predetermined amonut due to network 90, there is noimmediate response by amplifier 6| to the changed conditions of balanceof network 63. As the temperature at 85 continues to increase and wiper55 becomes more and more negative relative to wiper 8?, the positivesignal impressed on input terminal 96 continues to diminish. When theunbalance of the network 63, due to the increasing resistance ofthermistor 8| is high enough to normally require movement of wiper 55 tothe extreme left of resistor 15 to rebalance the same,

any further unbalance of the network due to further increase inresistance at 8| will result in wiper 45 becoming negative relative towiper 81. Assuming that this condition does take place, and theresistance of 8| does increase sufliciently to cause wiper 45 to becomenegative to wiper 87, a negative signal is impressed on amplifier ill bya circuit previously traced and the motor 44 is operated in a directionreverse from that previously described. The resulting clockwisedirection of operation of motor means 44 moves damper 42 in an openingdirection and permits cooling air to flow through aftercooler 40to'lower the tem- ,When this movement is suiiicient, and wiper 45 is nolonger negative with respect to 81, then the signal to the amplifierstops, the motor stops and there is no further adjustment of damper 42.If the initial opening movement of damper 42 is sumcient toprovideenough cooling of the air passing through the aftercooler 40 toprevent a further rise in temperature at 8|, the apparatus will remainstabilized. Assume that the aircraft is operating at near full power,however, and the temperature at M continues to rise to that wiperresistor 15. While network 53 has thus become more and more unbalanceddue to the increasing resistance at M, wiper more negative with respectto 31. 55 becomes more negative with respect to wiper 87 then wiper 95is positive with respect to wiper 55, then the signal added by networkis overcome and a negative signal is impressed on input terminal fromwiper 55. When this hap- When wiper pens, amplifier 5| energizes motormeans 54 in a manner to cause rotation opposite in direction from thatpreviously described. This causes motor means 54 to operate damper 52through linkage 53 in a clockwise direction and permits air flow throughexpansion turbine means 50 with a consequent diminishing of the flowthrough bypass M. of wiper 55 across resistor 15 and, in addition,causes rotation of cam means 58 which tilts mercury switch 51. As anytilting of mercury switch 51 opens its contacts and thereby deenergizesnetwork 90, the additive positive signal which previously made terminalas of the amplifier considerably positive with respect to wiper 55 isnow removed. Instead of a small negative signal being impressed onamplifier 5| which was merely the difference between the totai negativeunbalance between wiper 55 and wiper 81 and the positive potentialexisting between wiper 55 and Wiper 95, the said negative signal nowreaches the full value of that existing between wiper 55 and wiper 81.This signal will be of such value that motor means 58 will not be ableto immediately rebalance the signal by moving 55 across resistor 15 anddamper 52 will tend to be driven to its opposite extreme. Consideringthis description on a step by step'basis, damper 52 would be driven toits opposite extreme and damper 42 would remain in its previous partlyopen position. As a. matter of practice, however, as damper 52 is movedto close ofi bypass 5| and permit full flow of air through expansionturbine 50, the said turbine is put into operation at a high level ofcapacity and immediately effects a reduction in air temperature atthermistor 8 I. With the air temperature at 8| being reduced, theresistance of thermistor 8| is decreased and network 63 thereby becomesless unbalanced. Only a relatively small decrease in unbalance ofnetwork 63 is required to again make wiper 45 positive with respect towiper 81 and thereby energize amplifier 60 in a manner to again causerotation of motor means 44 in a clockwise direction until such op=eration is prevented by stop means of the motor. This causes closing ofthe damper 42 and thereby transfers all the cooling loadto the expansionturbine means 50. With a lower temperature at 8| and with wiper 55 beingadvanced across 45 tends to be driven further across 55 has become moreand This also causes a leftward movement" resistor to the left, thenetwork 63 not only becomes less unbalanced but the signal impressed onamplifier 6! is diminished due to the rebalancing effect of wiper 55moving to the left across the said resistor 15. When wiper '55 movessuiticiently to reach the same potential as wiper M, and thereforesupply no signal to amplifier iii, motor means 54 will stop. Thus, ifthe expansion turbine means 50 is able to bring the tempera ture ofthermistor 3i down to the desired value, it will now carry the entirecooling load.

-f the heat of the air being delivered through duct ii is soconsiderable that lull operation or" expansion turbine lift is unable toeffect a reduction in temperature at ill, the network will remainunbalanced and, assuming that the ternperature and resistance or"continues to in crease, wiper will become (or remain) nega tive relativeto wiper ti thereby causing operation of motor means i t in clockwisedirection to further open damper to drive wiper 45 to the left acrossresistor '13. As wiper ill moves to the left across resistor it, itbecomes less negative relative to resistor ill-7 and may again rebalancethe network in the manner previously described to remove the signal toamplifier fill. At Whatever point this takes place, damper :32 will thenremain in its adjusted position until there. is a further change intemperature at thermistor 8 i. It is thus apparent that the initialcooling load is taken by a partial operation of heat exchanger M, afurther increase in heat load is taken by expansion turbine 5b with theturbine assuming all of the load if it is possible for it to handle thesame and, if the load be ex-- cessive, both the expansion turbine Eliand aftercooler may be used up to their full capacity for effecting areduction in air temperature at ill.

During this discussion, it has been assumed that the temperatureremained unchanged in cabin Ill of the aircraft. Further, since the temperature in cabin 60 remained unchanged, wiper was maintained in itsprevious adjustment wherein it established a control point for network63 of about 125 degrees. However, as the aircraft ascended, the heatload on cabin ill would naturally tend to increase and the temperaturetherein therefore would tend to fall. As the temperature decreases incabin ill, the resistance of thermistor ill is diminished, the potentialof output terminal approaches that of input terminal Hi4 and thereforeterminal l l l becomes negative with respect to wiper l l2. Thisimpresses a negative signal on amplifier Jill which causes energizationof the amplifier winding of motor 34 in a direction to rotate wiper itto the right across resistor 82!. As wiper lilz moves to the rightacross resistor ltl, it becomes less positive with respect to terminal 6l l to rebalance the network. in a manner previously described. Whencompletely rebalanced, no further signal is furnished the amplifier androtation oi motor means 34 stops. However, as wiper H2 is adjusted tothe right across resistor l2 1 a new control point is established fornetwork 63 by the adjustment of wiper 3'! to the right acrossresistor83, this occurring because wiper 8'! is carried on shaft 33 of motormeans 3%.

Movement of wiper ill to the right across re sistor 83 tends to make itnegative with respect to wipers and and thereby requires a highertemperature at 8! to restore the balance of the network. This results ina higher temperature of the air being delivered to cabin it to supplythe needed heat due to the positive signals im- I pressed on theamplifiers and 81 causing operation of motors H and 54 in a damperclosing direction as previously described. In addition to. wiper 37being adjustedto the right, cam ii is also rotated'but, due to theextent of low portion 36, there is no immediate effect on the adjustmentof controller l1 and a minimum air flow is still maintained to thecabin. However, if the temperature in the cabin should continue to drop,network llliz would continue to become unbalanced causing rotation ofmotor meansfl-i to drive wiper i it further to the right across resistorto re balance the said network. This would also cause wiper to be drivenfurther to the right across resistor 83 and still further increase thetemper ture of the air being delivered to the cabin. However, thiscannot go on indefinitely for even though more heat may be needed in thecabin, there is a limit to the temperature of hat can be supplied to aninhabited cabin. when the air temperature reaches a mined high value,such as 250 degrees, no rdrtlier increase in temperature of the air iscalled for but continued rotation of shaft 33 brir :5 high portion 35 ofcam 3! under follower 32. to there by increase the tension on spring 28and thus increase the pressure differential that is to be maintainedacross venturi to. The demand increased pressure differential bycontroller ll results in an opening movement of damper in a mannerpreviously described with the result that a greater quantity of air atthe max-ah mum temperature is now being delivered to cabin to to meetthe increased demand. The increased quantity of air is supplied to thecabin at the expense of engine output for it is noted that all the airused by the cabin is that which could otherwise be used by the powerplant. With a proper design, it is only under adverse conditions thatboth maximum temperature and maximum air flow would be required tomaintain a suitable temperature such as 65 degrees in the cabin oi thecraft.

If it be assumed that the conditions which brought on the extreme heatload in the aircraft cabin were those occasioned by a high speed flightat low altitude on a warm day, it is obvious that the conditions willtend to become less severe and the apparatus will be readjusted for lessdrastic conditions as the aircraft ascends to higher elevations and acooler ambient.

Assumingthat the aircraft has started a relatively slow descent fromvery high elevations, and the power requirements for the power planthave been very greatly diminished, the lessened operation of the powerplant results less compressing of the air and consequently less he or"compression being added to same. 5:. suming that there had beensufllcient heating of the air to require damper $2 of aftercooler to tobe opened to some extent and expansion turbine to be in full operation,the diminished air temperature, and as further cooled by aftercooler illand turbine 50 results in a considerable drop in temperature atthermistor 8i. The effect of this i to unbalance the bridge in a mannerto first close damper 52 and then to gradually close damper 52 in amanner previously described. "While it was pointed out previously that arather large unbalance of a network was required to move damper 52 fromthe position shown due to network 90, once the expansion turbine 50 isput in operation and with the contacts of switch 5? opened, damper 52will be adjusted to control the entire cooling load as the loaddiminishe:

until the contacts of switch 51 are again closed when damper 52 reachesthe position shown in the drawing, that is in which all the air passingthrough duct II is bypassed through i. This method of operation ofexpansion turbine works well in practice for, while a relatively largeair flow is required to bring the expansion turbine into operation, amuch smaller flow of air can maintain its operation.

If the aircraft should now descend to a relatively low elevation, wherethere is a relatively high ambient temperature, it is of course obviousthat the heating load of the cabin .will be greatly diminished. As thecabin temperature tends to increase, and the resistance value oftermlstor l l I increases, contact Ill becomes positive relative towiper I I2 and motor 34 is energized in a manher to drive wiper H2 tothe left across resistor Mil. As wiper H2 is moved tothe left acrossresistor |2l to rebalance the network I02, it is of course obvious thatwiper 81 will be moved to the left across resistor 83 and cam 3| will berotated correspondingly. As wiper 87 is moved to the left acrossresistor 83, it establishes a progres sively lower control point fornetwork 63. Further, as it moves to the left, it tends to becomepositive relative to wipers 45 and or, otherwise stated, the said wipers4'5 and 55 tend to become negative relative to wiper 81. As noted, whennegative signals areimpressed on amplifiers and 6! by wipers i5 and 55respectively, motors id and 54 are controlled in a manner to providemore cooling. In addition, of course, the resulting movement of themotors tends to drive the wipers to the left across their respectiveresistors and thus rebalance the network. Should the temperature incabin l0 tend to rise, in spite of the cooler air being delivered to thesame, network l02 will again become unbalanced and cause operation ofmotor 34 in a direction to drive wiper M2 further to the left acrossresistor llH. As before noted, when the temperature in cabin Ill reaches80 degrees, wiper H2 must be at the left extreme of resistor I2 I to balnce the network, and wiper 81' is driven to the left extreme of resistor83. The demand for more cooling in cabin l0 thus requires a lower andlower temperature for the air being delivered to the said cabin.However, as it is not satisfactory to deliver air to the cabin at lowerthan 40 degrees, network 63 is so adjusted that the lowest control pointthat can be established by leftward movement of wiper 8! across resistor83 is 40 degrees and further rotation of the said wiper causes nofurther decrease in control point. However, a further rotation of shaft33 again advances high portion 35 of cam 3i under follower 32 and againtightens spring 28 of controller II. This requires an added rate of airfiow through venturi IE to stabilize controller il hence it is notedthat in the case of excessively high temperatures in the cabin, air willbe furnshed to the same at the lowest feasible temperature and at anincreased rate of flow in the same manner that maximum heat loadconditions were met while on the heating cycles for the said cabin.

It is thus noted that the present apparatus controls the rate of airflow to an aircraft cabin to a minimum value under most conditions andvaries the temperature of the air supplied to the cabin from a minimumrequired for a maximum cooling load to a maximum temperature such asrequired for a maximum heating load. The terns perature of the airsupplied to the cabin and the rate of flow of the same is determined bythe temperature existing in the cabin; further, when the air at aminimum rate of flow and at a temperature within the desired range isunable to meet the requirements of the cabin, the rate of airflow isthen increased to provide either more cooling or more heating asdesired.

From a study of the present specification, it is obvious that manysubstitutions and equivalents are feasible. For instance, a mass airflow sensing'device such as a Thomas type fiowmeter may be used forcontrolling damper l3 instead of venturi I 6 and differential pressurecontroller I l as shown. In addition, motors and motor controllingamplifiers or other relay apparatus may be used instead of that shownand described, and shaft 83 may be directly rotated in response to cabintemperature conditions by a bimetal device, a bulb-bellows thermostat orthe-like. In addition, while the present apparatus has been specificallydescribed in an application to an aircraft, it is equally applicable toany situation wherein there is adequate waste heat for heating andadequate cooling means available, such as may be found on a railwaytrain or in ship use. Be-

cause of the wide range of equivalents and substitutions that can bemade in the present system, I wish to be limited only by the appendedclaims. I

I claim as my invention:

1. In an aircraft having acabin, means for compressing air for saidcabin, conduit means for conducting said air to said cabin, means re-.sponsive to the rate of air flow through said conduit means, valvemeans for controlling said air flow, said valve means being controlledby said rate of flow responsive means, said conduit means includingaftercooler means, means for passing cooling air thorugh aftercoolermeans,

means for controlling the said flow of cooling air, said conduit meansalso including refrigerating means downstream of said aftercooler meansand bypass means around said refrigerating means, diverting means forcontrolling air ilow through said refrigerating means and said bypassmeans, means responsive to the temperature of the air discharged fromsaid conduit means into said cabin for controlling said cooling aircontrolling means and said diverting means in a sequence to lower thedischarge air temperature wherein the aftercooler is first used for aportion of its capacity, the refrigerating means is next used with theaftercooler, .followed by use of the refrigerating means alone and thenby the refrigerating means and the aftercooler together, and meansresponsive to the cabin temperature for adjusting said rate of flowresponsive means and said discharge air temperature responsive means.

2. In an aircraft having a cabin, means for compressing air for saidcabin, the said compressing means adding heat to said air, conduit meansfor delivering the compressed air to said cabin, adjustable means forcontrolling the rate of flow through said conduit means, controllableaftercooler means for cooling the air flowing through said conduit,controllable refrigerating means for cooling the air flowing throughsaid 'conduit means, adjustable means responsive to the temperature ofthe air discharged into said cabin for sequentially controlling saidaftercooler means and said refrigerating means, and means responsive tothe cabin temperature for adjusting said air flow controlling means andsaid discharge temperature responsive means.

3. In an aircraft having a cabin, means for compressing air for the saidcabin, the said compressing means adding heat to said air, conduit meansfor delivering said air to said cabin, said conduit includingaftercooler means, refrigerating means and bypass means around saidrefrigerating means, said aftercooler means being cooled by flow of coolair through the same, means for regulating the flow of said cool air,damper means for controlling the flow of compressed air through saidrefrigerating means and said bypass, adjustable means for regulating thequantity of air flow through said conduit means, means responsive to thetemperature oi the air discharged from said conduit means into saidcabin for sequentially controlling said damper means and said c001 airregulating means, motor means for adjusting said temperature responsivemeans and said quantity regulating means, and means responsive to thetemperature of said cabin for controlling said motor means.

i. In control apparatus of the sort described, a first motor means foroperating a condition changing device, a second motor means'ioroperating another condition changing device, amplifier means forcontrolling said first motor means, amplifier means for controlling saidsecand motor means, an electrical network capable of having its balancechanged by variations in the condition changed by said devices, a pairof voltage dividing follow-up potentiometers each having a resistor,said network including the resistors of said pair of follow-uppotentiometers series, one of said follow-up potentiometers beingadjustable by said first motor means and the other potentiometer beingadjustable by said second motor means, means connecting said networkincluding said one potentiometer in controlling relation to theamplifier for the first motor means, means including voltage addingmeans connecting said network and said other potentiometer incontrolling relation to the amplifier for said second motor means, andswitch means operable by said second motor means for controlling saidvoltage adding means.

5. In control apparatus, a plurality of devices to be controlled. anelectrical network circuit for seonentially controlling said devices,said network including a plurality of potentiometers each adjustable byone of said devices, means for altering the sequence of control or saiddevices, and means operated by one of said devices for controlling saidaltering means.

6. In control apparatus, a plurality of motor means to be controlled, apotentiometer for each of said motor means, each of said potentiometerseluding a resistor, an electrical network circuit including theresistors of said potentiometers series, means connecting said networkand the respective potentiometers in control of each of said motormeans, means interposed between one of said potentiometers and one orsaid motor means for opposing the controlling effect of said network onsaid one motor means, and switch means operable by said one motor meansfor controlling saicl interposed means.

'7. in control apparatus, a plurality of delib vices to be operated in apredetermined sequence,

amplifier means for controlling the energization of each of saiddevices, an electrical network including a potentiometer for each ofsaid devices, said potentiometers each being adjustable in accordancewith its respective device, means connecting each of said potentiometersin controlling relation to the amplifying means for the respectivedevice, one of said connecting means including a resistor in series withsaid amplify-' ing means and its controlling potentiometer, means forimposinga predetermined electrical potential across said resistor, andmeans operated by one of said devices for controlling said elect ricalpotential.

3. In control apparatus, a plurality of devices to be operated insequence, an electrical network for controlling said devices to operatein a predetermined sequence, an additional electrical network connectedto the first named network for preventing one of said devices fromoperating in said predetermined sequence, and means operated by said onedevice for altering the eiiect of said additional network.

9. in control apparatus for a space, means for circulating a conditionchanging medium to the space, means for controlling the rate of saidcirculation, means including adjustable means responsive the temperatureof the air supplied to said spam for controlling the temperature saidmedium, and means responsive to the temperature in said space forcontrolling said ad justable means and said rate controlling means.

10. In control apparatus, a plurality of devices to be operated, afollow-up potentiometer for each of said devices, each mtentiometerincluding a resistor, means including an electrical network circuit forcontrolling the operation of said devices, said network circuitincluding in series the resistors of said follow up potentiometers foran additional network means comprising a resistor and-means for causingan electrical potential across the same connected between one of saidfollow-up potentiometers and its respective device, and means operatedby the said respective device for controlling the said electricalpotential.

ll. in an aircraft propelled by a power plant including a gas turbineand an air compressor for the same and having a pressurized cabinwherein the air for said cabin is delivered through a conduit from thecompressor of said turbine to said cabin, in combination, means forcontrolling the rate of flow through said conduit, means for controllingthe temperature of the air discharged from said conduit into said cabin,and means responsive to the temperature of said cabin for controllingsaid rate of flow controlling means and said discharge temperaturecontrolling means. I

12. In an aircraft propelled by a power plant including an aircompressor and having a pressurized cabin wherein the air for the saidcabin is delivered through a, conduit from the compressor to said cabin,in combination, adjustable means for controlling the rate of flowthrough said conduit, adjustable means for controlling the temperatureof the air discharged from said conduit into said cabin from apredetermined high value to a predetermined low value, and meansresponsive to the temperature of cabin for adlusting said howcontrolling means and said discharge temperature controlling means sothat a high rate of flow and an extreme discharge temperature will berequired for an extreme temperature in said cabin and so that a minimumrate of air flow will be required for intermediate temperature conditionin said cabin.

13. In apparatus for maintaining the temperature of a space within apredetermined range, means for supplying a temperature changing mediumto said space, means for controlling the rate of supply of said mediumfrom a predetermined high value to a predetermined lower value, meansfor controlling the temperature of said medium 17 from an extreme highvalue above said range to an extreme low value below said range, meansresponsive to the temperature of said space and operative to adjust saidrate of supply means to said high value and said temperature controllingmeans to an extreme value when the temperature of said space is at anextreme of said range and to adjust said rate of supply means to a lowervalue when the temperature of said space is at a value intermediate saidrange.

14. In condition controlling apparatus for a space, means for supplyinga condition changing medium to said space, means for controlling therate of supply of said medium from a predetermined high value to apredetermined lower value, means for controlling a condition of saidmedium from a predetermined high value to a predetermined lower value,and means responsive to the space condition for adjusting said ratecontrolling means and said medium condition controlling means to a highrate of supply and an extreme value of the condition of said medium whenthe condition of said space is at an extreme.

15. In an aircraft propelled by a power plant including a gas turbineand an air compressor for the same and having a pressurized cabinwherein the air for the said cabin is delivered through a conduit meansfrom said compressor to to the temperature in said cabin for adjustinthe first named electrical network.

16. In control apparatus, means for supplying a medium to a space, saidmedium initially having an excess of heat, means for cooling said mediumto'remove said excess heat, means for controlling said cooling means,means for controlling the rate of supply of said medium to said space,and means responsive to the temperature of said space for regulatingsaid cooling control means and said rate controlling means, said rate ofsupply being normally maintained at a predetermined value and increasedupon either excessively low or high space temperatures.

17. In control apparatus for a space, means for supplying a conditionchanging medium to said space, means for varying the condition changingability of said medium between predetermined limits, and means forregulating the rate of supply of said medium to a predetermined valuewhen the condition changing ability of said medium is intermediate saidlimits and changing said rate of supply to a difierent value'when saidcondition changing ability is at either of said limits.

HUBERT T. SPARROW.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,168,680 Nordgren Aug. 8, 19392,180,764 Nessell Nov. 21, 1939 2,266,238 Newton Dec. 16, 1941 2,293,557Newton Aug. 18, I942 2,337,410 Peters Dec. 21, 1943 2,408,699 SparrowOct. 1, 1946 2,412,110 Williams Dec. 3, 1946

